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eventfs: Implement eventfs dir creation functions
Add eventfs_file structure which will hold the properties of the eventfs files and directories. Add following functions to create the directories in eventfs: eventfs_create_events_dir() will create the top level "events" directory within the tracefs file system. eventfs_add_subsystem_dir() creates an eventfs_file descriptor with the given name of the subsystem. eventfs_add_dir() creates an eventfs_file descriptor with the given name of the directory and attached to a eventfs_file of a subsystem. Add tracefs_inode structure to hold the inodes, flags and pointers to private data used by eventfs. Link: https://lkml.kernel.org/r/1690568452-46553-5-git-send-email-akaher@vmware.com Signed-off-by: Ajay Kaher <akaher@vmware.com> Co-developed-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Tested-by: Ching-lin Yu <chinglinyu@google.com> Reported-by: kernel test robot <lkp@intel.com> Closes: https://lore.kernel.org/oe-lkp/202305051619.9a469a9a-yujie.liu@intel.com Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
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‎fs/tracefs/Makefile‎

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# SPDX-License-Identifier: GPL-2.0-only
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tracefs-objs := inode.o
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tracefs-objs += event_inode.o
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obj-$(CONFIG_TRACING) += tracefs.o
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‎fs/tracefs/event_inode.c‎

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// SPDX-License-Identifier: GPL-2.0-only
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/*
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* event_inode.c - part of tracefs, a pseudo file system for activating tracing
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*
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* Copyright (C) 2020-23 VMware Inc, author: Steven Rostedt (VMware) <rostedt@goodmis.org>
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* Copyright (C) 2020-23 VMware Inc, author: Ajay Kaher <akaher@vmware.com>
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*
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* eventfs is used to dynamically create inodes and dentries based on the
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* meta data provided by the tracing system.
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*
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* eventfs stores the meta-data of files/dirs and holds off on creating
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* inodes/dentries of the files. When accessed, the eventfs will create the
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* inodes/dentries in a just-in-time (JIT) manner. The eventfs will clean up
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* and delete the inodes/dentries when they are no longer referenced.
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*/
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#include <linux/fsnotify.h>
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#include <linux/fs.h>
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#include <linux/namei.h>
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#include <linux/workqueue.h>
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#include <linux/security.h>
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#include <linux/tracefs.h>
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#include <linux/kref.h>
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#include <linux/delay.h>
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#include "internal.h"
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struct eventfs_inode {
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struct list_head e_top_files;
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};
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/**
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* struct eventfs_file - hold the properties of the eventfs files and
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* directories.
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* @name: the name of the file or directory to create
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* @list: file or directory to be added to parent directory
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* @ei: list of files and directories within directory
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* @fop: file_operations for file or directory
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* @iop: inode_operations for file or directory
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* @data: something that the caller will want to get to later on
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* @mode: the permission that the file or directory should have
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*/
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struct eventfs_file {
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const char *name;
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struct list_head list;
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struct eventfs_inode *ei;
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const struct file_operations *fop;
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const struct inode_operations *iop;
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void *data;
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umode_t mode;
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};
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static DEFINE_MUTEX(eventfs_mutex);
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static const struct inode_operations eventfs_root_dir_inode_operations = {
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};
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static const struct file_operations eventfs_file_operations = {
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};
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/**
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* eventfs_prepare_ef - helper function to prepare eventfs_file
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* @name: the name of the file/directory to create.
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* @mode: the permission that the file should have.
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* @fop: struct file_operations that should be used for this file/directory.
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* @iop: struct inode_operations that should be used for this file/directory.
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* @data: something that the caller will want to get to later on. The
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* inode.i_private pointer will point to this value on the open() call.
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*
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* This function allocates and fills the eventfs_file structure.
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*/
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static struct eventfs_file *eventfs_prepare_ef(const char *name, umode_t mode,
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const struct file_operations *fop,
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const struct inode_operations *iop,
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void *data)
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{
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struct eventfs_file *ef;
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ef = kzalloc(sizeof(*ef), GFP_KERNEL);
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if (!ef)
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return ERR_PTR(-ENOMEM);
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ef->name = kstrdup(name, GFP_KERNEL);
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if (!ef->name) {
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kfree(ef);
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return ERR_PTR(-ENOMEM);
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}
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if (S_ISDIR(mode)) {
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ef->ei = kzalloc(sizeof(*ef->ei), GFP_KERNEL);
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if (!ef->ei) {
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kfree(ef->name);
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kfree(ef);
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return ERR_PTR(-ENOMEM);
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}
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INIT_LIST_HEAD(&ef->ei->e_top_files);
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} else {
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ef->ei = NULL;
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}
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ef->iop = iop;
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ef->fop = fop;
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ef->mode = mode;
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ef->data = data;
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return ef;
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}
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/**
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* eventfs_create_events_dir - create the trace event structure
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* @name: the name of the directory to create.
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* @parent: parent dentry for this file. This should be a directory dentry
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* if set. If this parameter is NULL, then the directory will be
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* created in the root of the tracefs filesystem.
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*
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* This function creates the top of the trace event directory.
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*/
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struct dentry *eventfs_create_events_dir(const char *name,
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struct dentry *parent)
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{
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struct dentry *dentry = tracefs_start_creating(name, parent);
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struct eventfs_inode *ei;
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struct tracefs_inode *ti;
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struct inode *inode;
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if (IS_ERR(dentry))
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return dentry;
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ei = kzalloc(sizeof(*ei), GFP_KERNEL);
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if (!ei)
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return ERR_PTR(-ENOMEM);
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inode = tracefs_get_inode(dentry->d_sb);
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if (unlikely(!inode)) {
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kfree(ei);
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tracefs_failed_creating(dentry);
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return ERR_PTR(-ENOMEM);
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}
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INIT_LIST_HEAD(&ei->e_top_files);
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ti = get_tracefs(inode);
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ti->flags |= TRACEFS_EVENT_INODE;
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ti->private = ei;
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inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
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inode->i_op = &eventfs_root_dir_inode_operations;
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inode->i_fop = &eventfs_file_operations;
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/* directory inodes start off with i_nlink == 2 (for "." entry) */
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inc_nlink(inode);
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d_instantiate(dentry, inode);
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inc_nlink(dentry->d_parent->d_inode);
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fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
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return tracefs_end_creating(dentry);
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}
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/**
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* eventfs_add_subsystem_dir - add eventfs subsystem_dir to list to create later
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* @name: the name of the file to create.
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* @parent: parent dentry for this dir.
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*
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* This function adds eventfs subsystem dir to list.
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* And all these dirs are created on the fly when they are looked up,
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* and the dentry and inodes will be removed when they are done.
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*/
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struct eventfs_file *eventfs_add_subsystem_dir(const char *name,
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struct dentry *parent)
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{
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struct tracefs_inode *ti_parent;
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struct eventfs_inode *ei_parent;
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struct eventfs_file *ef;
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if (!parent)
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return ERR_PTR(-EINVAL);
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ti_parent = get_tracefs(parent->d_inode);
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ei_parent = ti_parent->private;
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ef = eventfs_prepare_ef(name, S_IFDIR, NULL, NULL, NULL);
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if (IS_ERR(ef))
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return ef;
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mutex_lock(&eventfs_mutex);
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list_add_tail(&ef->list, &ei_parent->e_top_files);
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mutex_unlock(&eventfs_mutex);
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return ef;
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}
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/**
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* eventfs_add_dir - add eventfs dir to list to create later
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* @name: the name of the file to create.
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* @ef_parent: parent eventfs_file for this dir.
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*
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* This function adds eventfs dir to list.
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* And all these dirs are created on the fly when they are looked up,
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* and the dentry and inodes will be removed when they are done.
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*/
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struct eventfs_file *eventfs_add_dir(const char *name,
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struct eventfs_file *ef_parent)
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{
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struct eventfs_file *ef;
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if (!ef_parent)
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return ERR_PTR(-EINVAL);
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ef = eventfs_prepare_ef(name, S_IFDIR, NULL, NULL, NULL);
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if (IS_ERR(ef))
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return ef;
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mutex_lock(&eventfs_mutex);
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list_add_tail(&ef->list, &ef_parent->ei->e_top_files);
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mutex_unlock(&eventfs_mutex);
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return ef;
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}

‎fs/tracefs/internal.h‎

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#ifndef _TRACEFS_INTERNAL_H
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#define _TRACEFS_INTERNAL_H
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enum {
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TRACEFS_EVENT_INODE = BIT(1),
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};
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struct tracefs_inode {
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unsigned long flags;
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void *private;

‎include/linux/tracefs.h‎

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#ifdef CONFIG_TRACING
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struct eventfs_file;
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struct dentry *eventfs_create_events_dir(const char *name,
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struct dentry *parent);
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struct eventfs_file *eventfs_add_subsystem_dir(const char *name,
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struct dentry *parent);
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struct eventfs_file *eventfs_add_dir(const char *name,
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struct eventfs_file *ef_parent);
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struct dentry *tracefs_create_file(const char *name, umode_t mode,
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struct dentry *parent, void *data,
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const struct file_operations *fops);

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